We have the problem with the dripping sound. Whenever we turn on the hot or cold water on in bathroom on the first or second floor, we can hear the dripping sound behind the wall. Usually lasts 5 min after we turn off the water. We checked all walls. Couldn't find anything. Not sure if should we spend money for plumbing inspection. What could the reason be for this dripping sound?
I would get it looked at, it could be one of 2 things in my opinion:
1: (the bad, but likely) you have a leak in the drain pipe.
2: (the good but unlikely) some sort of build-up is causing a dripping down the inside of a vertical pipe.
In the long run it WILL cause damp related problems such as rot and smells...